What the Numbers Mean

By Aaron Gold

When you’re reading about cars, you’re going to run into engine specifications, i.e. a 2.0 liter 4-cylinder turbo producing 160 horsepower and 175 lb-ft of torque. Cylinders? Torque? What do all those numbers mean? That’s the subject of this VroomGirls University lesson.

CYLINDERS

A cylinder is the power unit of an engine; it’s the chamber where the gasoline is burned and turned into power. (For more on what goes on inside the cylinders, see How Engines Work.) Most cars and SUV enginess have four, six, or eight cylinders. Generally, an engine with more cylinders produces more power, while an engine with fewer cylinders gets better fuel economy.

Cylinders will either be arranged in a straight line (an inline engine, i.e. “inline 4”, “I4” or “L4” ) or in two rows (a V engine, i.e. “V8”).

DISPLACEMENT (Liters and Cubic Inches)

Engines are measured by displacement, usually expressed in liters (L) or cubic centimeters (cc). Displacement is the total volume of all the cylinders in an engine. An engine with four cylinders of 569cc each totals 2276cc, and will be rounder off and referred to as a 2.3 liter engine. Larger engines tend to produce more power — specifically more torque (see below) — but use more fuel.

Up until the early 1980s, engines were measured in cubic inches. One liter equals about 61 cubic inches, so a 350 cubic inch engine is about 5.7 liters.

TURBOCHARGERS

A turbocharger is a device that is used to boost the power of an engine. A four-cylinder engine with a turbocharger can produce as much power as a six-cylinder engine, but uses less fuel when driven gently. (For more information, see How Turbochargers and Superchargers Work.) Engines with a turbo sometimes get a T after their displacement; “2.0T” denotes a 2-liter engine with a turbocharger.

HORSEPOWER AND TORQUE

Horsepower and torque measure the amount of power an engine develops, with horsepower being the most commonly-used measurement. The difference between horsepower and torque is widely misunderstood (and difficult to explain).

Torque, which is measured in pound-feet (lb-ft or ft-lbs), measures pulling power; when you step on the gas pedal and the seat pushes into your back, you are feeling torque. Trucks need lots of torque to get their heavy loads moving. Horsepower is a function of torque and engine speed (RPM), and indicates how much sustained work the car can do. Racing cars need high horsepower to maintain high speeds. Generally, bigger-displacement engines develop more torque, but small engines can spin faster, which increases their horsepower output.

A car with high horsepower but low torque may feel sluggish from a stop, but will feel stronger as the engine spins faster and faster. A high-torque, low-hp engine will accelerate strongly from a stop, but will trail off as the engine speeds up (until the transmission shifts gears).

Horsepower and torque measurements are “peak” numbers; a 180 horsepower engine will only produce 180 horsepower at a certain engine speed — say, 6,000 RPM. At other speeds, the engine develops less horsepower. The same goes for torque, although some engines (especially those with turbochargers) have a sustained peak-torque range, developing their rated torque between, say, 1,800 and 4,000 RPM. An engine with strong mid-range torque (peaking between 2,000 and 4,000 RPM) will have good passing acceleration, while lot of low-end torque (below 1,500 RPM) is useful for towing trailers or driving off-road. However, cars with high-torque engines are more likely to slip and slide in rain and snow.

All that said, other factors, such as how much the car weighs, will affect acceleration. How the vehicle feels when you drive it is more important than the horsepower and torque ratings.

I appreciate the information, but still have a question – currently car shopping (compact to midsize SUV) and I’m stuck on the cylinders. I need a car that can accelerate quickly (esp. from a stopped position) – I was adamant about getting a V6, but now that I’m considering a compact suv and most have a V4 engine, is that enough? Should I focus on horsepower instead? (I’m assuming 4 cylinders are sufficient for smaller suvs due to lighter weight?) Look forward to hearing your opinion. Thank you!

Try the Ford Escape or Lincoln MKC. They have the new Ford Eco-Boost engines that use 4 cylinders with turbochargers to get good gas mileage without losing horsepower. Plus they look great! I am planning on buying a 2016 Lincoln MKC myself.

To accelerate quickly you would need more torque. Horsepower is the Rotations Per Minute or R.P.M.’s Your car needs to exert a certain amount of power, so technically while you would have a higher top speed with more horsepower, you would not be “accelerating” very fast witout enough torque, but too much torque will cause your wheels to spin out, so:

Torque: How fast you get to a certain speed or how fast your wheels are spinning

Horsepower: The top speed of your car or how fast you can actually go.

A V4 Would be more fuel efficient, but would not accelerate as quickly or have as much horsepower for the simple fact that there are less cylinders and less volume to be filled with oxygen and gas. A turbocharger or supercharger (forced induction) will allow you to gain both torque and horsepower, and allow your V4 engine to produce the same power output as the V6, ir even twice the output of your engine itself, it would not be as big as a V6, but it would be cheaper, but adding forced induction to a V6 can make it more efficient at low rpm as well as twice the power as the engine itself if tuned correctly. There are many many many factors you have to take in to persoective when using forced induction such as the size of the turbo or supercharger, the cooling method used (air or intercooler), how many cylinders you car has and what type inline or v shape, the wastegate, oil lines, and water coolants that you may want to use. Over all, if you do you research and find a good tuber shop or aftermaket shop around where you are, you coukd serioisly turbi your v4 for faster acceleration without having to put in a lot of money for the v6.

Excellent article. I really thought the explanation was great. A couple of comments, though:

I think there is a mistake in “… engines were measured in cubic inches. One liter equals about 61cc, so a 350 cubic inch engine is about 5.7 liters.” I think it should be: “engines were measured in cubic inches. One liter equals about 61ci”

Also, it would be useful to understand a little more about how to compare displacement and power. Often, a user is exposed to power when purchasing a new vehicle or lawn appliance. Sometimes the measurement of effectiveness of the device is given in power, while sometimes the displacement is listed. These aren’t really convertable, but it would be nice to understand a bit about how much power I’m getting, in general, if I purchase a 90cc lawn mower. 😉

I need something with AWD due to the weather, but also something that can get out of the way/merge quickly as I drive on congested freeways. I was looking at crossovers and compact sedans, what I see tends to be in the range of around 145@4200 (Torque) and 148@6200 (Horsepower) OR 185@4800 (Torque) and 204@6400 (Horsepower).

It seems like, for my purposes, the range of 145@4200 for torque is probably better?

I am confused about one thing and it isn’t explained in the why can you have a challenger hellcat with a v8 engine that has 700 hp the you have say a Audi R8 with a v10 and it only has 520 hp is this a thing to do with patens or is a way to balence the wait if someone could explain that would be great Thanks:)

Okay, let’s look at some specs. The 2016 Dodge Challenger Hellcat has a 6.2 liter supercharged V8 engine with 707 horsepower and 650 lb-ft of torque. The 2016 Audi R8 has a 5.2 liter naturally-aspirated V10 engine with 533 horsepower and 398 lb-ft of torque. I myself am a bit surprised at the power figures of the Audi R8, but you have to take in mind that the Audi R8 is only naturally-aspirated, meaning that it has no supercharger or turbocharger. The Dodge Challenger Hellcat, on the other hand, has a supercharger, allowing it make more horsepower and torque. The Hellcat also has more liters of displacement, allowing it to use more fuel.

A car with high torque at low to middle engine speeds (1500 to 4000 RPM) will produce more power in that engine speed range. This is good for people who like their car to accelerate strongly without having to make the engine roar to get good acceleration. On the other hand, a smaller engine car even with the same peak horsepower as the high torque car, will need to brought up to high engine speed any time it needs decent acceleration. Cars with low torque but high peak horsepower engines, need to downshift on even the slightest inclines and need to shift down 2 or more gear to pass another car. Such highly strung engines may be a fun novelty for a while for a 17 year old boy racer, but it gets old very fast. So pick a high torque engine if you want good power and acceleration at normal engine speeds and pick a smaller, lower torque, higher horsepower engine if you only want good acceleration power at high engine speeds and don’t mind the transmission constantly changing gears to keep up with traffic – such engines will feel weak below 4000 rpm.

I am old school. I have no clue as to what 2.0 liter or what ever means. I evaluate by 0 – 60 in how many seconds. To me a car that takes 14 seconds to do this is not fast as a matter of fact correct me if I am wrong you have to almost push it up to the top of a hill. If a car does 0 – 60 in 8 sec it has some guts no speed demon, if you do it in 5 or under you have the need for speed.

Now I am not up to date (my current car is 18 years old) tells you how much I love dealing with car sales people but why is there not an interpretation mandatory of dealerships that talk your language that you understand instead of talking a language you have no clue about what it is saying.

Very good, I could make a distinction between the “High revving RPM engine” being able to sustain higher horsepower and it still could have a relatively smaller displacement than, say, a “muscle car” engine that has a lower RPM limit and accelerates faster from a standpoint but has certain difficulties with achieving higher speed. As a car enthusiast, I prefer a “middle of the road” kind of vehicle, being capable of having a descent top speed and also descent torque, followed by the engine that could theoretically produce more HP but less torque. I’m no fan of gas-guzzling muscle cars because of the fuel price of where I live.

Before purchasing a car, we should first keep some valuable things in our mind such as; features, engine capacity, design, performance and mileage. But the most efficient part if engine section; we should go for efficient engine and its features which consist of turbochargers, good horsepower and many others. So that, we can get a good driving experience.

Thanks for the article, interesting stuff, but my question is unanswered… actually I may be asking something that doesn’t make sense sooo.

What’s the relationship between displacement and hp? Is there a simple formula for a rough (educated) guess?

I’m guessing it’s not a direct relationship between cc and hp, pretty sure it’s not actually… we used to own a 6cyl 3.4L impala (567cc/cyl) with 180hp, and just now in the news I saw a mazda racer 4cyl 2L (500cc/cyl) that puts out 600(!!)hp, from a 2liter engine! Oookay, so larger displacement doesn’t necessarily mean more hp.

So then the question becomes how is displacement important? It’s always one of the first numbers you get when hearing about a car, but it seems to be an essentially useless metric, it doesn’t really mean anything other than what it says.